An epoxy group-bearing organopolysiloxane or organosilane is prepared by effecting addition reaction between SiH groups on an organohydropolysiloxane or organohydrosilane and alkenyl groups on an alkenyl group-bearing epoxy compound in the presence of a catalyst.
During this addition reaction, polymerization reaction of epoxy groups can take place as a side reaction, resulting in a reaction product having a substantially increased viscosity or being gelled. The thickening and gelation become outstanding particularly when the alkenyl group-bearing epoxy compound is added dropwise to a mixture of the organohydropolysiloxane and the addition reaction catalyst, or when the addition reaction catalyst is added to a mixture of the organohydropolysiloxane and the alkenyl group-bearing epoxy compound to conduct batch reaction.
One known process of preparing an epoxy group-bearing organopolysiloxane while suppressing polymerization of epoxy groups involves mixing a SiH group-bearing silane or siloxane with a tertiary amine and a hydrosilylation catalyst, and reacting the mixture with an olefin epoxide to produce an epoxy silicone (see JP-A 6-32906). While the epoxy silicone is often used in such an application as a coating to be cured with an acid generator, typically an onium salt, this process has a possibility that the tertiary amine be left in the epoxy silicone and restrain the silicone from being cured with the acid generator.
It is also known from JP-A 6-136126 to prepare an epoxy silicone by effecting addition reaction between an organohydrogensiloxane or organohydrogensilane and an ethylenically unsaturated epoxide in the presence of a hydrosilylation catalyst comprising a phosphine ligand and a phosphine-free transition metal complex. Depending on the amount of the phosphine ligand relative to the phosphine-free transition metal complex, there can arise a problem that gelation occurs due to the polymerization of epoxy groups or the addition reaction does not proceed at all.
Therefore, an object of the invention is to provide a novel and improved process for preparing an epoxy group-bearing organopolysiloxane or organosilane through addition reaction between an organohydropolysiloxane or organohydrosilane and an alkenyl group-bearing epoxy compound while avoiding the undesired phenomenon of gelation or thickening.